The international criminal court's move to indict the president of Sudan, Omar al-Bashir, for war crimes and crimes against humanity is a historic decision with serious implications for political leaders, now in office or recently retired, and not only in Africa, who have ignored human rights and the laws of war in pursuit of contentious, arguably illegal military campaigns.

But momentous though it certainly is, in practice the ICC's action is unlikely to have much immediate impact in terms of putting Bashir in the dock in The Hague or improving the plight of Darfur's 2.7 million displaced people. Sudanese officials warn that, on the contrary, it could rally support for Bashir domestically while emboldening Darfur rebel groups to step up the violence.

"The court made clear that heads of state are not beyond the reach of the law," said Juan Mendez, president of the International Centre for Transitional Justice in New York. "It is telling the world that government leaders can and should be held accountable for their actions ... We know from history that silence in the face of atrocities does not prevent further crimes."

A request for full co-operation in securing Bashir's arrest directed to all 108 state parties to the ICC's founding treaty formed part of today's ruling. But the pre-trial judges and chief prosecutor Luis Moreno-Ocampo may find they are whistling in the wind. A statement by foreign secretary David Miliband, while supportive of the court's action, made no mention of practical steps – such as sanctions or travel bans – that Britain or its EU partners may take to enforce it.

Speaking off the record, western diplomats admitted the arrest warrant could compound an already "difficult and complicated situation" in Sudan – and that the consequences, for western embassy employees, UN peacekeepers and aid agency staff were entirely unpredictable. Rather than launching into hot pursuit of Bashir, the aim in the next few days would be "to keep the temperature down," a diplomat said.

Similar caution was evident in the initial response of the Obama administration, despite its theoretically more activist stance on Darfur since taking over from George Bush. Officially, US policy in Sudan, like just about everywhere else, is under review. Today the state department confined itself to the anodyne hope that "those who have committed atrocities should be brought to justice".

Suggestions that Bashir will be pursued through the UN security council, which created the ICC, also seemed wide of the mark. Russia, a permanent, veto-wielding member, warned that the warrant created "a dangerous precedent in international relations" and could further destabilise Sudan and the region. Khartoum also says China, the biggest outside investor in Sudan's oil industry, has given assurances that it will block "politicisation" of the Bashir case in the security council.

Having had months to plot a response to the ICC, Sudanese diplomats are now intent on actively increasing, and exploiting, both western political dithering and the genuine international worries about possible wider, negative consequences.Khartoum plans to ignore the warrant and stick to a policy of "business as usual", a senior diplomat said. "We are going to concentrate on things that really matter – development, the Darfur peace talks, the elections, and implementing the [north-south] Comprehensive Peace Agreement".

At the same time the government will go on the offensive, a close adviser to Bashir said. The first step will be to rally support on the streets, although demonstrations will not be deliberately targeted at western embassies or the UN, he said. Second, it will do all it can to discredit the ICC and Moreno-Ocampo.

Third, Khartoum expects the African Union to issue a statement of solidarity, similar to that agreed at its recent Addis Ababa summit. Support is also confidently expected from developing countries in the Group of 77 and from the Arab League and Islamic Conference, the adviser said.

As an earnest of Khartoum's intent, Bashir's spokesman confirmed the president would attend an Arab summit in Qatar this month as planned. So far at least, Bashir clearly has no fear of arrest while travelling abroad. Given yesterday's largely mealy-mouthed statements by western governments, and the broader worries about destabilising Sudan, his current calculations are probably correct.